Prototype f64x2.trunc on ARM for both ARM v7 and ARM v8. ARM v8 has
support for vrintz, and for ARM v7 we fallback to runtime.

Since ARM v8 uses vrintz, which is the same instruction used for F64
trunc (scalar), wasm-compiler reuses the Float64RoundTruncate check.

Bug: v8:10553
Change-Id: I074d5b4172809915d4b37c59bd3b0dcbf9a45e1d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2268357
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68592}